Ok... so basically you've got a bio steps filter thing, a pump, an air pump w/stones and some water conditioner ...

So first off, the bad news...

If you indeed ordered the 3500 GPH pump, you're wayyyyyyy too big for the filter and U/V you have coming. A 9W UV won't do anything when the flow rate is that high, plus, the flow rate exceeds what the filter will handle as well. Keep that bigger pump for later or return it and I would suggest this pump - Tiny Might Pump - Tiny Might Also, get a strainer basket to keep the gnarlies out of the pump if possible. I think this one will work - Leaf Traps - External Pond Pumps You'll have to bump up the fitting on the pump from 1" to 1 1/2" but that's easy with a bushing.

This will still put you at the top end for flow rate but you'll probably be achieving a turnover rate for your pond of 1 per hour which is OK as long as you don't get carried away with feeding...

Now... the rest of it. Knowing where you're at and what you've got I would do the following:

Get a piece of 2" pvc pipe about 5' long. Cut a slot length wise through it but don't cut to the end of the pipe. This slot will be the intake of the pump. My best guess would be to start at about a 2' slot in the middle of the pipe. What you're trying to do is match the amount of water the slot can provide to the pump without cutting too much so that it only pulls from one end of the slot. (if that makes any sense) You want the slot in the middle and your suction to run the length of it. Use a reasonable thick blade so you have about a 1/4" slot. One end will go into the bulkhead (with appropriate fitting installed) and the other end gets a 90 degree elbow that is plugged and cut down some so that the pipe sits slot side down and slightly off the bottom of the pond... about 1/2" off the bottom would be good. This will give the pump the best chance at pulling the crap from the pond bottom.

Then on the dry side connect the pump w/leaf basket to the bulk head and from the pump into the filter, then return to pond. Try and place the water fall so that it creates a circular current in the pond, this will aid in moving the poop to the middle to get picked up by the slot.

Your filter will get filthy quick because you're emulsifying the fish poop with your pump so you'll have to clean it out very regularly. (again, feeding will dictate your schedule but plan on a daily cleaning of the mats in the filter). You'll get a good idea real quick of how often this is required after a short time.

Put the airstones in the tank with the pump connected but keep in mind where you put these things. They will draw poop to them and your goal is to have the PVC pulling in all the poop. Don't put them by the PVC pipe though as you will end with cavitation in your pump more than likely with all the air it will suck. If there is a spot in the filter you can put these airstones, that would be better. Ideally I would try and get them into the filter as your bacteria will have a greater air demand than your koi. Try stuffing them down between the mats at about the middle. The first few mats will just bung up with crap and any bio you get will do better towards the last few mats. Give these ones the additional air if possible.

Your water fall will provide sufficient O2 to the water provided temps don't get too high. (say.... 75 degrees or less and you should be fine)

Oh, and all the check valve stuff... Basically, these pumps can't pump air. So if you were to install the pump above the water line it would require a pump that could "lift" the water up and then into circulation. Since you'll be installing the pump on the ground below the water level, you won't need a check valve for it. With the plumbing and pump below the water line your pump will always be filled with water; "primed".

I hope this helps,

Grant

Hey Grant,

Can I put pre-filtration system into this QT tank with BIO filter and the pump. Do you have any recommandation for indoor QT heater or where to get them with reasonable price.